In the treatment of wastewater, it is known in the industry to use aeration equipment in order to aerate and mix the wastewater. This aeration equipment may be positioned generally at the bottom of the wastewater basin at an intermediate level in the basin, or allowed to float on the surface of the wastewater reservoir. It is common to use submerged diffusers capable of discharging air into the treatment basin. An example of a particularly effective diffuser is a flexible membrane diffuser. U.S. Pat. No. 5,846,412 issued to Tharp provides an example of an air diffuser and mounting arrangement for use in a water treatment system.
One arrangement for aerating and mixing large wastewater basins makes use of a large number of diffusers contained in separate multi-diffuser modules in a grid pattern throughout the basin. The aeration equipment typically includes a large capacity gas supply source for supplying air to the diffusers. Each individual diffuser is connected to the main air supply conduit via a branch conduit with the diffusers appropriately located throughout the basin to provide thorough mixing and aeration.
When many individual diffusers are positioned in a grid pattern to aerate a large wastewater treatment reservoir, general maintenance and repair become problematic. Locating and retrieving an individual diffuser module is difficult for a variety of reasons. Mechanical retrieval can be expensive and cumbersome, requiring massive cranes to pull each module up from the bottom of the basin. Modules may be located in the center portion or a far-side portion of the basin where they cannot be accessed at all by a crane. In large basins, many modules are inaccessible even to cranes with lengthy booms.
After the repair or maintenance is completed, the individual modules must be placed back in position on the bottom surface of the basin, again with a crane. In order to position the module in the proper orientation on the bottom surface of the basin, the module should not appreciably tip or roll during its descent, which might result in the structure landing improperly on its side or planing sideways during descent. Likewise, if a module is removed from a diffuser grid structure, it should be carefully repositioned within the pattern of the grid. The module should be lowered steadily over its position within the grid, preferably with the module being maintained substantially horizontal as it descends.
In some applications, the main air supply pipes or laterals float on the surface with large diffuser modules suspended from them above the bottom of the basin. The modules are typically suspended on a plurality of flexible air supply lines attached to the floating air laterals. Retrieval of these large diffuser modules in this type of system presents the same types of problems as with bottom mounted modules.